The present invention relates to a positive photosensitive polyimide composition, insulation film formed therefrom and to a method for forming insulation film pattern using the same.
Photosensitive resin compositions are classified into A) polarity-changing type wherein the polarity of the exposed regions is changed so that the solubility thereof is changed, B) cutting type wherein chemical bonds are cut by exposure and the exposed regions are solubilized, and C) cross-linking type wherein cross-linking reaction proceeds so that exposed regions are insolubilized. The polarity-changing type may be used as either positive working or negative working composition depending on the composition of the developing solution. The cutting type may be used as positive working composition, and the cross-linking type may be used as negative working composition in theory. The cross-linking type photosensitive materials have a disadvantage in carrying out microscopic processing with high resolution that the exposed regions are swollen by the developing with an organic solvent.
In recent years, the molding materials used for overcoating flexible printed circuits, interlayer insulation films of multilayer substrates, insulation films and passivation films of solid elements in semiconductor industry, as well as the interlayer insulation materials of semiconductor integrated circuits and multilayer printed circuit boards are demanded to have good heat resistance. Further, the need to attain higher densification and higher integration demands photosensitive heat-resisting materials.
The semiconductor substrates which are used as semiconductor integrated parts in microelectronic industry are covered with photoresists. Photoresist relief structures are formed by forming images and subsequent development of the photoresist layers. The relief structures are used as the masks for preparing circuit patterns on the semiconductor substrates. By this processing cycle, the relief structure of a microchip can be transferred to a substrate.
Photoresists include two different types, that is, positive working photoresist and negative working photoresist. These are different in that the exposed regions of the positive working photoresist is removed by development so that the non-developed regions are left on the substrate, while the exposed regions of the negative working photoresist are left as the relief structure. The positive working photoresists have intrinsically high image resolutions so that they are suited for production of VLSIs (large scale integrated circuits).
Conventional positive working photoresists contain a type of novolak resin which is soluble in aqueous alkali and a photosensitive quinone diazide which decreases the solubility of the resin in alkali. When the photoresist layer is irradiated, the quinone diazide is photoexcited so as to be converted to carboxylic acid, so that the solubility in alkali of the exposed regions is increased. Thus, by developing the photoresist with an aqueous alkali, a positive working photoresist relief structure is obtained (U.S. Pat. No. 36,664,735 etc).
The characteristics of the photoresist compositions used in industries are the solubility of the photoresist in the solvent to be applied, the photosensitization rate of the photoresist, the developing contrast, the solubility of the developing solution acceptable from the view point of environment, adhesiveness of the photoresist, dimensional stability at high temperatures, and abrasion resistance.
The photoresist relief structures obtained by the exposure and development are usually subjected to heat treatment (postbake) at a temperature of 120xc2x0 C. to 180xc2x0 C. The purpose of this treatment is to promote the adhesiveness of the photoresist with the substrate, curing of the photoresist structure, and removal of all of the remaining volatile components to decrease the erosion in the subsequent etching step.
However, in plasma etching, the substrates are subjected to a temperature higher than 200xc2x0 C. The photoresists containing as the base a novolak resin and a stabilizing improver cannot be thermally stabilized at a temperature of not lower than 180xc2x0 C.
Polyimide resins are resistant to high temperature of about 400xc2x0 C. and are stable to chemicals. Therefore, they are useful in forming heat-resisting photoresist layers,
Conventional polyimide photoresists are negative-type photoresists. The system of the negative-type photoresists is based on polyamic acid polymer having photoreactive side chains. However, this basic material has problems in that it has a poor storage stability, a very slow sensitizing rate, and an excess structural shrinkage after development and curing (the rate of shrinkage after baking is about 60%). With this composition, to attain a high resolution, exposure of about 10 minutes is necessary. Further, high concentration solutions thereof for forming thick films have especially poor storage stabilities.
With positive-type photoresists, high resolution is attained, exposure time is short and developing properties with alkali are excellent. Positive working high temperature type photoresist having phenol group was developed. A polyoxazole precursor was synthesized by the reaction between 3,3xe2x80x2-dihydroxy-4,4xe2x80x2-diaminobiphenyl and isophthalic acid dichloride. This composition is mixed with o-quinone diazide or naphthoquinone diazide to form a high sensitive positive working photosensitive polyoxazole precursor, and polyoxazole having a heat resistance and mechanical properties comparable to those of polyimide membrane is formed after processing (U.S. Pat. No. 4,339,521 and U.S. Pat. No. 4,395,482).
A solvent-soluble polyimide was synthesized by the reaction of hexafluoro-2,2-bis(hydroxyaminophenol)propane with hexafluoro-2,2-bis-(dicarboxyphenyl)propane dianhydride (6FDA) or with 3,4,3xe2x80x2,4xe2x80x2-benzophenone tetracarboxylic acid dianhydride (BTDA) or with 5,5xe2x80x2-oxy-bis-1,3-isobenzofurandione (4,4xe2x80x2-oxydiphthalic acid dianhydride), and positive working photosensitive polyimides were prepared by mixing the polyimides and o-naphthoquinone diazide, respectively. In this method (Japanese Laid-open Patent Application (Kokai) No. 64-60630 and U.S. Pat. No. 4,927,736), the fluorine atom-containing polyimides are soluble in polar solvents. A novel method in which polyimide solutions are directly formed by heating the polyimide at 140 to 160xc2x0 C. in the presence of p-toluene sulfonic acid as a catalyst was employed. However, to separate the catalyst and the polyimide, a method in which the polyimide solution is poured into methanol to recover the polyimide resin as precipitates and the precipitates are re-dissolved, is employed, which method is unsuitable for industrial application.
Phenol group or carboxyl group is protected with tetrahydro-2H-pyranyl group to vanish the solubility in alkali. By adding a photoacid generator to the resultant and by irradiating the resulting composition with light, an acid is generated. By this acid, the block of the hydroxyl group or carboxyl group is decomposed so that the material is converted to soluble in alkali. By carrying out heat treatment after exposure, a plurality of blocks are catalytically removed by the acid, so that an amplification effect is obtained, thereby the composition is highly sensitized (T. Omote et al.; Macromol., 23, 4788 (1990), K. Naitoh et al.; Polym. Adv. Technol. 4, 294 (1993), K. Naitoh et al.; J. Photopolym. Sci. Technol. 4, 294 (1993), T. Yamaoka et al.; Photosensitive Polyimides Fundamental and Application, 177-211, Technomic Publish Company Inc. USA(1995)).
A positive-type photosensitive polyamic acid was reported, wherein the carboxyl group of polyamic acid is converted to ester of 2-nitrobenzyl alcohol to prevent dissolution in alkali, and upon irradiation with light, the ester of the 2-nitrobenzyl group is decomposed to generate a carboxylic acid so that the compound is converted to soluble in alkali (S. Kubota et al.; J. Macromol. Sci. Chem. A24 (10) 1407 (1987), Ao Yamaoka et al.; Polyfile 2, 14(1990)).
An object of the present invention is to provide a photosensitive polyimide composition which is soluble in organic solvents, which excels in adhesiveness, heat resistance, mechanical properties and flexibility, which shows properties of alkali-soluble highly sensitive positive-type photoresist upon irradiation with light.
The present inventors intensively studied to discover that, by combining a solvent-soluble polyimide and a photoacid generator, a highly sensitive positive-type photosensitive polyimide composition which is alkali-soluble upon irradiation with light is obtained, and that the insulation film made of the positive-type photosensitive polyimide composition excels in adhesiveness, heat resistance, mechanical properties and flexibility, thereby completing the present invention.
That is, the present invention provides a positive-type photosensitive polyimide composition comprising photoacid generator and solvent-soluble polyimide which shows positive-type photosensitivity in the presence of the photoacid generator. The present invention also provides a positive-type photosensitive resin film prepared by making the above-mentioned composition, according to the present invention, dissolved in a solvent, into the form of film. The present invention also provides a polyimide insulation film having a pattern, which is prepared by coating, on a substrate, the above-mentioned composition, according to the present invention, dissolved in a solvent, drying the composition, exposing an image pattern on the composition to irradiation with light or electron beam, and removing the exposed regions with an alkaline developing solution. The present invention further provides a method for forming a polyimide insulation film pattern comprising coating the composition on a substrate, according to the present invention, drying the composition, exposing an image pattern on the composition to irradiation with light or electron beam, and removing the exposed regions with an alkaline developing solution.
By the present invention, positive-type photosensitive polyimide compositions which are alkali-soluble upon irradiation with light were provided. The positive-type photosensitive polyimide compositions according to the present invention have high sensitivities. That is, with the polyimide compositions according to the present invention, very high imaging resolutions are attained. The insulation films made from the positive-type photosensitive polyimide compositions according to the present invention are excellent in adhesiveness, heat resistance, mechanical properties and flexibility. Therefore, the insulation films are of polyimide having high heat resistance, electric insulation and adhesiveness, so that they may be widely used in the field of production of semiconductors, electronic parts and the like.
As mentioned above, the positive-type photosensitive polyimide composition according to the present invention comprises a photoacid generator and a solvent-soluble polyimide which shows positive-type photosensitivity in the presence of the photoacid generator.
The term xe2x80x9cphotoacid generatorxe2x80x9d herein means a compound which generates an acid upon irradiation with light or electronic beam. Since the polyimide is decomposed by the action of the acid and is soluble in alkalis, the photoacid generator employed in the present invention is not restricted and any compound which generates an acid upon irradiation with light or electron beam may be employed. Preferred examples of the photoacid generator include photosensitive quinone diazide compounds and onium salts.
Preferred examples of the photosensitive quinone diazide compounds include esters of 1,2-naphthoquinone-2-diazide-5-sulfonic acid and 1,2-naphthoquinone-2-diazide-4-sulfonic acid, the counterparts of the esters being low molecular aromatic hydroxyl compounds such as 2,3,4-trihydroxybenzophenone, 1,3,5-trihydroxybenzene, 2-methylphenol, 4-methylphenol and 4,4xe2x80x2-hydroxy-propane. Preferred examples of the onium salts include aryl diazonium salts such as 4(N-phenyl)aminophenyl diazonium salt; diaryl halonium salts such as diphenyl iodonium salt; triphenyl sulfonium salts such as bis{4-(diphenylsulfonio)phenyl}sulfide, and bis-hexafluoroantimonate, but the preferred onium salts are not restricted to these.
The polyimide contained in the polyimide composition according to the present invention consists essentially of one or more aromatic diamine components and one or more aromatic acid components, and is produced by direct imidation reaction between one or more aromatic diamines and one or more aromatic tetracarboxylic dianhydrides.
Preferred examples of the aromatic diamine components (described in the form of monomers) constituting the polyimide contained in the polyimide composition according to the present invention include 4,4xe2x80x2-diaminodiphenyl ether, 3,4xe2x80x2-diaminodiphenyl ether, bis(4-phenoxy)1,4-benzene, bis(4-phenoxy)1,3-benzene, bis(3-phenoxy)1,3-benzene, 2,2-bis(4-aminophenyl)propane, 1,1,1,3,3,3-hexafluoro-2-bis(4-aminophenyl)propane, 4,4xe2x80x2-diaminophenylmethane, bis(4-aminophenoxy)4,4xe2x80x2-diphenyl, 2,2-bis{(4-aminophenoxy)phenyl}propane, 2,2-bis{(4-aminophenoxy)phenyl}hexafluoropropane, 1,3-diaminobenzene, 1,4-diaminobenzene, 2,4-diaminotoluene, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminobiphenyl, 2,2xe2x80x2-bis(trifluoromethyl)benzidine, xcex1,xcex1xe2x80x2-bis(4-aminophenyl)-1,4-diisopropylbenzene, bis(4-aminophenoxy)-1,3-(2,2-dimethyl)propane and diaminosiloxane. These aromatic diamine components may be employed individually or in combination.
Preferred examples of the aromatic acid components (described in the form of monomers) constituting the polyimide contained in the polyimide composition according to the present invention include 3,4,3xe2x80x2,4xe2x80x2-benzophenone tetracarboxylic dianhydride, 3,4,3xe2x80x2,4xe2x80x2-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 3,4,3xe2x80x2,4xe2x80x2-biphenyl ether tetracarboxylic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 2,3,5,6-pyridine tetracarboxylic dianhydride, 3,4,3xe2x80x2,4xe2x80x2-biphenylsulfone tetracarboxylic dianhydride, bicyclo(2,2,2)-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 4,4xe2x80x2-{2 and 2,2-trifluoro-1-(trifluoromethyl)ethylidene}bis(1,2-benzene dicarboxylic dianhydride). These aromatic acid components may be employed individually or in combination.
It is preferred to employ one or more aromatic diamines, which have one or more carbonyl groups, nitro groups, methoxy groups, sulfonic groups, sulfide groups, anthracene groups or fluorene groups (hereinafter referred to as xe2x80x9cphotosensitive aromatic diaminexe2x80x9d), as the one or more aromatic diamines constituting the polyimide, because they are easily photoexcited upon irradiation with UV after adding a photoacid generator, so that images can be formed with high sensitivity and high resolution with smaller dose of irradiation.
As the preferred photosensitive aromatic diamines, firstly, dialkyl-diamino-bisphenyl sulfone and dialkoxy-diamino-biphenyl sulfone such as 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diamino-biphenylsulfone and 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diamino-biphenylsulfone are exemplified. The polyimides containing such biphenyl sulfones are linear polymers having high mechanical strengths and high moduli of elasticity, so that they are studied as highly elastic polyimide fibers, and also as gas separation membranes because they can be made into films. They can be used as fibers or films, and also as photosensitive films. As shown in the Examples below, these polyimides containing biphenyl sulfone do not show photosensitivity even if Michler""s ketone which is a sensitizer or a radical generator is added. It was discovered, however, that they are soluble in alkalis by irradiation with light after adding a quinone diazide compound. Even if the molecular weight (based on polystyrene) is changed to 30,000, 50,000 and 100,000, the polyimides are soluble in alkalis. From this fact, it is thought that the quinone diazide is photodecomposed to generate a radical and simultaneously to be converted to indene acid, and the product interacts with the polyimide groups and biphenyl sulfone groups, so that the polyimide is converted to be alkali-soluble. That is, by UV irradiation, the quinone diazide compound is photodecomposed and indene acid is further generated. As a result, the alkyl group or alkoxy group on the biphenyl group is activated so that the sulfone bond is cleaved, and indene acid is added thereto, thereby increasing the solubility of the polyimide in alkalis.
Additional preferred examples of the photosensitive aromatic diamines include 9,9-bis(aminophenyl)fluorene and 9,9-bis(aminoalkyl-phenyl)fluorene. The polyimides containing such fluorenes are linear polymers having high mechanical strengths and high moduli of elasticity, so that they are polyimides having excellent film properties, and having excellent properties when formed into gas separation membranes. They can be used as fibers or films, and also as photosensitive films. As shown in Examples below, these polyimides do not show photosensitivity even if Michler""s ketone which is a sensitizer or a radical generator is added. It was discovered, however, they are converted to be soluble in alkalis by irradiation with light after adding a quinone diazide compound. Even if the molecular weight (based on polystyrene) is changed to 30,000, 50,000 and 100,000, they interact with the radical and the acid produced by photolysis of the quinone diazide to form alkali-soluble polyimides, which give clear positive-type images. More particularly, 9,9-bis(aminophenyl)fluorene is synthesized from fluorenone and aniline in the presence of an acid catalyst (Beilstein 13,III,548a). Fluorenone is a photosensitizer which is used as widely as Michler""s ketone and benzanthrone. Although fluorenone-containing polyimides are sensitized by irradiation with light, they are usually not photodecomposed. It was discovered, however, if a quinone diazide co-exists, the quinone diazide generates a radical by irradiation with light, and radical becomes indene acid that interacts with the polyimide, so that the bis(aminophenyl)fluorene-containing polyimides are soluble in alkalis. This is presumably because that the SP3 carbon structure at the 9-position of the bis(aminophenyl)fluorene group in the polyimide chain is temporarily stabilized by resonance and is changed to SP2 carbon structure, so that the aniline group is eliminated and the polyimide chain is cleaved. Various fluorenone derivatives are known. For example, there are 2-nitro compounds, 2,7-dinitro compounds and 7-chloro compounds. Similarly, as for aniline, various derivatives such as 2-methylaniline and 2-methoxyaniline are known. From the above-described fluorenone derivatives and the aniline derivatives, various 9,9-bis(aminophenyl)fluorene derivatives are produced in the presence of an acid catalyst. These derivatives also constitute positive-type photosensitive compositions. By using benzathrone compounds in place of the fluorenone, positive-type photosensitive polyimide compositions are also obtained.
Additional preferred examples of the photosensitive aromatic diamines are nitro aromatic diamines. In 1,4-diamino-2-nitrobenzene and/or 3,3xe2x80x2-dinitro-4,4xe2x80x2-diaminobiphenyl, the O atom of nitro radical interacts with the N atom of imide bond. Nitro group and benzene ring are excited by electron resonance upon irradiation with light, and the oxygen atom in the nitro group acts on the N atom in the imide group to increase the electron effect. It is presumed that the proton generated from the diazoquinone by light irradiation attacks the N atom in the imide bond to cut the imide bond to generate amide bond, and thus the polyimide is soluble in alkalis. Preferred examples of the nitro aromatic diamines include 1,4-diamino-2-nitrobenzene, 1,5-diamino-2-nitrobenzene, 3-nitro-4,4xe2x80x2-diaminobiphenyl, 3,3xe2x80x2-dinitro-4,4xe2x80x2-diaminobiphenyl and the like. Among these, 1,4-diaminonitrobenzene and 3,3-dinitro-4,4xe2x80x2-diaminobiphenyl are especially preferred.
Another preferred example of the photosensitive aromatic diamines is 1,5-diaminoanthraquinone. In 1,5-diaminoanthraquinone-containing polyimides, the anthraquinone is easily photoexcited. It is presumed that the carbonyl radical of imide bond exerts electron effect to carbonyl radical in anthraquinone, that the proton generated from the diazoquinone by light irradiation attacks the N atom in the imide bond to cut the imide bond to generate amide bond, so that the polyimide is soluble in alkalis. Anthraquinone is also a photosensitizer and positive-type patterns are effectively formed with small dose of energy irradiation. Compounds which have similar action to that of 1,5-diaminoanthraquinone include 2,4-diaminoacetophenone, 2,4-diaminobenzophenone, 2-amino-4xe2x80x2-aminobenzophenone, 2-amino-5-aminofluorenone and the like, and these compounds may be employed. Preferably, 1,5-diaminoanthraquinone is used.
Additional preferred examples of the photosensitive aromatic diamines include diphenyl sulfide group-containing diamines such as 4,4xe2x80x2-diaminodiphenyl sulfide. In this case, the diphenyl sulfide group is contained in the main chain. It is presumed that the diphenyl sulfide in the main chain of the polyimide generates an acid upon irradiation with light in the presence of a quinone diazide and the acid is bound to the sulfide group so as to convert the sulfide group to thiol, which is alkali-soluble. The diphenyl sulfide groups in the main chain of the polyimide may be those originated from a diamino compound such as 4,4xe2x80x2-diaminodiphenyl sulfide, 3,4xe2x80x2-diaminodiphenyl sulfide, 4,4xe2x80x2-diamino-3,3xe2x80x2-dimethyl sulfide, bis(4-aminophenoxyphenyl) sulfide, thionine or the like. Among these, 4,4xe2x80x2-diaminodiphenyl sulfide which is easily available and which is highly effective is preferred.
Additional preferred examples of the photosensitive aromatic diamines are diphenyl disulfide group-containing diamines such as 4,4xe2x80x2-diaminodiphenyl disulfide. In this case, the diphenyl disulfide is contained in the main chain. It is thought that the polyimides containing diphenyl disuslfide in the main chain easily bind to the proton generated from the quinone diazide by irradiation with light so as to be converted to two thiol molecules. In fact, disulfide compounds are more easily cleaved than sulfide compounds and give sharper patterns. The diphenyl disulfide in the polyimide main chain may be originated from a diamino compound such as 4,4xe2x80x2-diaminodiphenyl disulfide, 3,4xe2x80x2-diaminodiphenyl disulfide, 4,4xe2x80x2-diamino-3,3xe2x80x2-dimethyl disulfide, bis(4-aminophenoxyphenyl)disulfide, thionine or the like. Among these, 4,4xe2x80x2-diaminodiphenyl disulfide which is easily available and which is highly effective is preferred.
Another preferred example of the photosensitive aromatic diamines is 9,10-bis(4-aminophenyl)anthracene. Solvent-soluble positive-type photosensitive polyimides containing 9,10-bis(4-aminophenyl)anthracene in the main chains are linear polymers having high mechanical strengths and high moduli of elasticity, so that they are studied as highly elastic polyimide fibers, and also as gas separation membranes because they can be made into films. They can be used as fibers or films, and also as photosensitive films. Anthraquinone is easily photoexcited upon irradiation with light, so that it is widely used as a sensitizer. It is presumed that 9,10-bis(4-aminophenyl)anthracene group is sensitized and activated upon irradiation with light, and if a quinone diazide exists, it interacts with the acid generated by the photolysis of the quinone diazide, so that the aminophenyl groups on the 9- and 10-positions are attacked by the proton so as to be eliminated from the anthracene group, thereby generating anthraquinone. It is presumed that, as a result, the polyimide is soluble in alkalis, so that clear positive-type images can be formed. As can be seen from the fact that anthraquinone is known as a sensitizer, the photosensitizing effect of this system is large, so that it is not necessary to co-employ a separate sensitizer. Positive-type patterns are effectively formed by irradiation of small energy for a short time.
Additional preferred examples of the photosensitive aromatic diamines are aromatic amines having biphenyl sulfone, such as 3,3xe2x80x2-diaminodiphenyl sulfone, 4,4xe2x80x2-diaminodiphenyl sulfone, bis-{4-(3-aminophenoxy)biphenyl}sulfone and bis{4-(4-aminophenoxy)biphenyl}sulfone. In this case, the biphenyl sulfone are contained in the main chain of the polyimide. The polyimides containing biphenyl sulfone are linear polymers having high mechanical strengths and high moduli of elasticity, so that they are studied as highly elastic polyimide fibers, and also as gas separation membranes because they can be made into films. They can be used as fibers or films, and also as photosensitive films. It was discovered as shown in the Examples below, that they are soluble in alkalis by irradiation with light after adding a quinone diazide compound. Even if the molecular weight (based on polystyrene) is changed to 40,000, 100,000 and 150,000, the polyimides are converted to be soluble in alkalis. From this fact, it is thought that the quinone diazide is photodecomposed to generate a radical and simultaneously to be converted to indene acid, and they interact with biphenyl sulfone photoexcited by irradiation with light so as to decompose the biphenyl sulfone to phenyl sulfonic acid, so that the polyimide is alkali-soluble. By UV irradiation, the quinone diazide compound is photodecomposed and indene acid is further generated. It is presumed that, as a result, the biphenyl group is activated and the sulfone bond is cleaved by the action of indene acid to produce phenyl sulfonic acid, thereby increasing the solubility of the polyimide in alkalis.
Additional preferred examples of the photosensitive aromatic diamines include bis{4-(4-aminophenoxy)phenyl}sulfone, bis{4-(3-aminophenoxy)phenyl}sulfone, o-tolidine sulfone, 4,4xe2x80x2-diaminobenzophenone, 3,3xe2x80x2-diaminobenzophenone, 2-nitro-1,4-diaminobenzene, 3,3xe2x80x2-dinitro-4,4xe2x80x2-diaminobiphenyl, 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diaminobiphenyl and 1,5-diaminonaphthalene.
The above-mentioned various photosensitive aromatic diamines may be employed individually or in combination.
By employing an aromatic diamine into which hydroxyl group, pyridine group, oxycarbonyl group or tertiary amine group is introduced (hereinafter also referred to as xe2x80x9calkali-solubility-increasing aromatic diaminexe2x80x9d), the aromatic diamine is bound to or interacts with the acid produced by the photoacid generator, so that positive-type images are more easily formed by alkali treatment.
As the preferred alkali-solubility-increasing aromatic diamines, firstly, diaminopyridine and diaminoacridinium are exemplified. Weakly basic pyridine groups contained in the polyimide main chain forms acid-base bond with the acid generated by UV irradiation of diazonaphthoquinone so that the polyimide becomes soluble in alkalis. The diaminopyridine in the main chain of the polyimide may be 2,6-diaminopyridine, 3,5-diaminopyridine, 3,5-diamino-2,4-dimethylpyridine and the like. Preferably, 2,6-diaminopyridine or 3,5-diaminopyridine is employed. As the compounds having pyridine ring, diaminoacridium may be used. For example, acriflavin, Acridine Yellow, proflavin and the like may be employed, and acriflavin is preferred.
Additional preferred examples of the alkali-solubility-increasing aromatic diamines are hydroxyl group-containing or alkoxyl group-containing aromatic diamines which are diaminodihydroxybenzene, diaminodihydroxybiphenyl or diaminodialkoxybiphenyl. These hydroxyl group-containing or alkoxyl group-containing aromatic diamines are preferably contained as one component in the polyimide containing not less than two types of aromatic diamine components. Preferred examples of these aromatic diamines include 1,4-diamino-2-hydroxybenzene, 3,3xe2x80x2-dihydroxy-4,4xe2x80x2-diaminobiphenyl and 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diaminobiphenyl. The hydroxyl groups and the methoxy groups in the polyimide main chain are bound to the acid produced by the light irradiation of the quinone diazide so that the polyimide is soluble in alkalis.
Another preferred example of the alkali-solubility-increasing aromatic diamines is 1,4-bis(3-aminopropyl)piperazine (hereinafter referred to as xe2x80x9cdiaminopiperazinexe2x80x9d). This is preferably contained in the polyimide main chain together with other aromatic diamine(s). The diaminopiperazine contained in the polyimide main chain together with the aromatic diamine(s) is a highly basic compound having two tertiary amines. Therefore, the piperazine group is bound to the carboxylic acid generated by light irradiation of the diazonaphthoquinone so as to form acid-base bond, so that the polyimide is soluble in alkalis.
Another preferred example of the alkali-solubility-increasing aromatic diamines is 3,9-bis(3-aminopropyl)2,4,8,10tetraoxaspiro-(5,5)-undecane. This is preferably contained in the polyimide main chain together with other aromatic diamine(s). Diaminotetraoxaspiroundecane is known to be decomposed by an acid to aldehyde and alcohol. It is presumed that the tetraoxaspiro group in the polyimide main chain of the polyimide containing diaminotetraoxaspiroundecane is decomposed by the action of the carboxylic acid generated by the light irradiation so that the polyimide is soluble in alkalis, thereby the polyimide shows the characteristics of positive-type photosensitive photoresists.
Additional preferred examples of the alkali-solubility-increasing aromatic diamines are acid amides of diaminobenzoic acid. In this case, the polyimide main chain preferably contains not less than two types of aromatic diamine components and one of them is acid amide of diaminobenzoic acid. Preferred examples of the acid amide of diaminobenzoic acid are morpholine amide and N-methylpiperazine amide of 3,5-diaminobenzoic acid. However, the acid amide of diaminobenzoic acid is not restricted thereto, and aliphatic primary, secondary and tertiary amines may be employed, and alcohols and aliphatic amines containing these bases may also be employed. Here, the number of carbon atoms in xe2x80x9caliphatic aminexe2x80x9d is not restricted, but about 2 to 6 is usually preferred.
Additional preferred examples of the alkali-solubility-increasing aromatic diamine are 3,5-diaminobenzoic acid and 2-hydroxy-1,4-diaminobenzene.
The above-described various photosensitive diamines, may be employed individually or in combination.
Use of the above-described photosensitive aromatic diamine and/or alkali-solubility-increasing aromatic diamine is not indispensable, and the polyimides constituted by the combination of the above-mentioned one or more aromatic diamine components and the one or more aromatic acid components may be employed. Especially, in cases where electron beam is used for exposure, good positive-type images may be formed with high sensitivity even without using the photosensitive aromatic diamine and/or the alkali-solubility-increasing aromatic diamine.
The diamine component of the polyimide may be constituted by the above-mentioned photosensitive aromatic diamine and/or alkali-solubility-increasing aromatic diamine alone, or the polyimide may contain the photosensitive aromatic diamine and/or alkali-solubility-increasing aromatic diamine together with the one or more of the above-described aromatic diamine components. The content of the photosensitive aromatic diamines and/or the alkali-solubility-increasing aromatic diamines based on the total aromatic diamine components is preferably 30 to 100 mol %, more preferably 50 to 100 mol %.
It should be noted that in the above-described various compounds and components containing alkyl groups or the alkyl moiety-containing groups, the number of carbon atoms in the alkyl groups or the alkyl moieties is preferably 1 to 6 unless otherwise specified. Further, as the aromatic ring, unless otherwise specified, benzene ring, naphthalene ring and anthracene ring as well as hetero rings of these rings are preferred.
The polyimide in the composition according to the present invention is solvent-soluble. The term xe2x80x9csolvent-solublexe2x80x9d means that the polyimide can be dissolved in N-methyl-2-pyrrolidone (NMP) at a concentration of not less than 5% by weight, preferably not less than 10% by weight.
The polyimide in the composition according to the present invention preferably has a weight average molecular weight based on polystyrene of 25,000 to 400,000, more preferably 30,000 to 200,000. If the weight average molecular weight is within the range of 25,000 to 400,000, good solubility in solvent good film-forming properties, high film strength and high insulation may be attained. Further, in addition to satisfaction of the above-mentioned range of the molecular weight, it is preferred that the thermal decomposition initiation temperature be not lower than 450xc2x0 C. from the view point of heat resistance.
The polyimide in the composition according to the present invention may be produced by direct imidation reaction between the aromatic diamine and the aromatic tetracarboxylic dianhydride. In the production of the conventional negative-type polyimide photoresists, a polyamic acid having photoreactive side chains are used. The polyamic acid is easily decomposed at room temperature, so that the storage stability is poor. Further, the photosensitive polyamic acid requires heat treatment at 250 to 350xc2x0 C. so as to carry out imidation reaction. In contrast, the polyimide in the composition according to the present invention is directly produced by the imidation reaction between the aromatic diamine and the aromatic tetracarboxylic dianhydride in solution, but not a polyamic acid, so that the production process thereof is largely different from that of the conventional negative-type polyimides.
The direct imidation reaction between the aromatic diamine and the aromatic tetracarboxylic dianhydride may be carried out using a catalytic system utilizing the following equilibrium reaction between a lactone, base and water.
{lactone}+{base}+{water}={acid}+{base}xe2x88x92
A polyimide solution may be obtained by using the {acid}+{base}xe2x88x92 system as a catalyst and heating the reaction mixture at 140-180xc2x0 C. The water produced by the imidation reaction is eliminated from the reaction system by azeotropic distillation with toluene. When the imidation in the reaction system is completed, {acid}+{base}xe2x88x92 is converted to the lactone and the base, and they lose the catalytic activity and are removed from the reaction system. The polyimide solution produced by this process can be industrially used as it is as a polyimide solution with high purity because the above-mentioned catalytic substances are not contained in the polyimide solution after the reaction.
Examples of the reaction solvent which may be used in the above-mentioned imidation reaction include, in addition to the above-mentioned toluene, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, sulfolane, tetramethylurea and the like.
As the lactone, xcex3-valerolactone is preferred. As the base, pyridine and/or methylmorpholine is(are) preferred.
The mixing ratio (acid/diamine) between the aromatic acid dianhydride and the aromatic diamine subjected to the imidation reaction is preferably about 1.05 to 0.95 in terms of molar ratio. Further, the concentration of the acid dianhydride based on the total reaction mixture is preferably about 4 to 16% by weight, the concentration of the lactone is preferably about 0.2 to 0.6% by weight, the concentration of the base is preferably about 0.3 to 0.9% by weight, and the concentration of the toluene is preferably about 6 to 15% by weight at the initiation of the reaction. The reaction time is not restricted and varies depending on the molecular weight of the polyimide to be produced and the like, and usually about 2 to 10 hours. It is preferred to carry out the reaction under stirring.
It should be noted that the production process per se of the polyimide using the binary catalytic system comprising the lactone and the base is known, and described in, for example, U.S. Pat. No. 5,502,143.
By carrying out the above-described imidation reaction sequentiality in two steps using different acid dianhydrides and/or different diamines, polyimide block copolymers can be produced. By the conventional process for producing polyimide through polyamic acid, only random copolymers can be produced as copolymers. Since polyimide block copolymers can be produced selecting arbitrary acids and/or diamines, desired properties or functions such as adhesiveness, dimensional stability, low dielectric constant and the like can be given to the polyimide. In the composition of the present invention, such a polyimide copolymer may also be employed.
A preferred process for producing the polyimide block copolymers include the process wherein a polyimide oligomer is produced using the acid catalyst generated by the above-described lactone and the base, and using either one of the aromatic diamine component or the tetracarboxylic dianhydride in excess, and then the aromatic diamine and/or the tetracarboxylic dianhydride is(are) added (the molar ratio of the total aromatic diamines to the total tetracarboxylic dianhydride is 1.05 to 0.95), thereby carrying out two-step polycondensation.
The photosensitive polyimide composition according to the present invention preferably contains the photoacid generator in an amount of 10 to 50% by weight based on the weight of the polyimide.
The photosensitive polyimide composition according to the present invention may be in the form of solution suited for application on substrates. In this case, as the solvent, a polar solvent such as N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, sulfolane, tetramethylurea or the like; which is used as the solvent for the imidation reaction, may be employed. The concentration of the polyimide in the solution may preferably be 5% to 50% by weight, more preferably 10% to 40% by weight. Since the polyimide obtained by the direct imidation using the catalytic system comprising the lactone and the base is obtained in the form of solution in which the polyimide is dissolved in the polar solvent, and since the concentration of the polyimide in the obtained solution is within the preferred range mentioned above, the polyimide solution produced by the above-described process may advantageously be used as it is. If desired, however, the produced polyimide solution may be diluted with diluent. As the diluent, a solvent which does not largely decrease the solubility, such as dioxane, dioxolane, xcex3-butyrolactone, cyclohexanone, propylene glycol monomethyl ether acetate, methyl lactate, anisole, ethyl acetate or the like may be employed, although the diluent is not restricted to these.
To make the composition of the present invention fitted to each final use, the sensitivity of the pattern resolution may be increased by giving a photosensitizer to the photosensitive polyimide of the present invention. Although not restricted, examples of the photosensitizer include Michler""s ketone, benzoin ether, 2-methylanthraquinone, benzophenone and the like. Further, modifiers which are added to the ordinary photosensitive polyimides, such as coupling agents, plasticizers, film-forming resins, surfactants, stabilizers, spectrum sensitivity-adjusters and the like may be added.
By applying the photosensitive polyimide composition of the present invention in the form of solution on a substrate, drying the composition, selectively exposing the composition, and developing the resultant, a polyimide membrane having an arbitrary pattern on the substrate can be formed. Alternatively, by forming a polyimide film from the polyimide composition by a conventional method such as extrusion, adhering the film on a substrate, selectively exposing the film and developing the resultant, a polyimide membrane having an arbitrary desired pattern on the substrate may be formed. Since such a polyimide membrane is resistant to heat and insulative, it may be used as an insulation membrane or dielectric layer in semiconductor devices as it is. Alternatively, it may be used as a photoresist for selectively exposing the substrate.
Examples of the substrate to which the photosensitive polyimide of the present invention is applied include semiconductor disks, silicon wafers, germanium, gallium arsenide, glass, ceramics, copper foil, printed boards and the like.
Coating of the composition may be carried out usually by dipping, spraying, roll coating, spin coating or the like. As for the adhesive films, products having uniform thickness may be usually obtained by employing thermocompression bonding. By employing these methods, the photosensitive polyimide according to the present invention may be effectively used for forming coating layers with a thickness of 0.1 to 200 xcexcm, or for forming relief structures.
The thin membranes in multilayered circuits used as temporary photoresists or as insulation layers or dielectric layers may preferably have a thickness of about 0.1 to 5 xcexcm. In cases where the membrane is used as a thick layer such as immobile layer, the thickness thereof may preferably be 10 to 200 xcexcm in order to protect the semiconductor memories from xcex1-ray.
It is preferred to carry out preheating at a temperature of 80 to 120xc2x0 C. after applying the photosensitive polyimide to the substrate. In this case, an oven or heating plate is used, and an infrared heater is preferably employed as the heater. The drying time in this case may be about 5 to 20 minutes.
Thereafter, the photosensitive polyimide layer is subjected to irradiation. Usually, UV light is used, but high energy radiation, such as X-ray, electron beam or high power oscillation beam from an extra-high pressure mercury lamp may be employed. Although irradiation or exposure is carried out through a mask, the surface of the photosensitive polyimide layer may also be irradiated withthe radiation beam. Usually, irradiation is carried out using a UV lamp which emits a light having a wavelength of 250 to 450 nm, preferably 300 to 400 nm. The exposure may be carried out using a single color ray or multiple color rays. It is preferred to use a commercially available irradiation apparatus, such as contact and interlayer exposing apparatus, scanning projector or wafer stepper.
After the exposure, by treating the photosensitive layer with a developer which is an aqueous alkaline solution, the irradiated regions of the photoresist layer can be removed, thereby a pattern is obtained. The treatment may carried out by dipping the photoresist layer or spraying the developer under, pressure to the photoresist layer so as to dissolve the exposed regions of the substrate. Examples of the alkali to be used as the developer include, although not restricted, aminoalcohols such as aminoethanol, methyl morpholine, potassium hydroxide, sodium hydroxide, sodium carbonate, dimethylaminoethanol, hydroxytetramethyl ammonium and the like. Although the concentration of the alkali in the developer is not restricted, it is usually about 30 to 5% by weight.
The development time varies depending on the energy of exposure, strength of the developer, manner of development, preheating temperature, temperature of the treatment with the developer and the like. Usually, with the development by dipping, the development time is about 1 to 10 minutes, and with the development by spraying, the development time is usually about 10 to 60 seconds. The development is stopped by dipping the developed layer in an inactive solvent such as isopropanol or deionized water, or by spraying such a solvent.
By using the positive-type photosensitive polyimide composition according to the present invention, polyimide coating layers having a layer thickness of 0.5 to 200 xcexcm, and relief structures having sharp edges may be formed.
Since the polyimide in the composition of the present invention is composed of complete linear polyimide, it is not changed in water or heating, and its storage stability is good. Therefore, it can be used as photosensitive films. Further, after forming the pattern by development, unlike the polyamic acid molecules, the postbake at 250 to 450xc2x0 C. is not necessary, and only drying under heat at 120 to 200xc2x0 C. to evaporate the solvent is carried out. Further, the polyimide membrane after forming the pattern is tough, resistant to high temperature and excellent in mechanical properties.
As for the photoresists comprising a novolak photosensitive material and a diazonaphthoquinone, it is said that both the resolution and sensitivity are excellent when the molecularxe2x80x2weight of the novolak is not more than 10,000, and is uniformed within the range of 5000 to 10,000.
Similarly, the resolution and photosensitivity of the positive-type photosensitive polyimides, as well as the heat resistance, chemical resistance and mechanical strength, are variable depending on the molecular weight and the molecular weight distribution. There is a tendency that the larger the molecular weight and the smaller the carboxylic acid content, the longer the development time and the dipping time in the alkali solution.
The present invention will now be described more concretely by way of examples. It should be noted, however, the following examples are presented for the illustration purpose only and should not be interpreted in any restrictive way. It is apparent for those skilled in the art that photosensitive polyimides having various characteristics are obtained by combination of various acid dianhydrides and aromatic diamines.